Pilot valve

ABSTRACT

The working piston of a pilot valve has an extremity formed with an axial bore which receives a pilot piston with two or three heads defining one or two peripheral recesses included in a throttled path for the controlled admission of high-pressure fluid to a peripheral shoulder on that extremity. An oblique passage, forming part of that fluid path, extends in the region of the peripheral shoulder within the body of the working piston. The selected position of the working piston is maintained by countervailing fluid pressure acting upon a land of this piston, the effective area of that land being half that of the peripheral shoulder which in a state of balance is subjected to half the countervailing fluid pressure.

O United States Patent 1 [111 3,722,547

Kirstein 1 Mar. 27, 1973 54] PILOT VALVE 3,339,573 9/1967 Bahniuk ..l37/625.64 x Inventor: Lothar Kirsten, Bad Kreuznach, 3,386,339 6/l968 Selsam ..137/625.6

Germany Primary ExaminerHenry T. Klinksiek [73] Assignee: Jos. Schneider & Co. Optische Assistant Examiner-Robert J. Miller Werke, Bad Kreuznach, Germany Attorney-Karl F. Ross [22] Filed: Oct. 18, 1971 The working piston of a pilot valve has an extremity formed with an axial bore which receives a pilot piston ABSTRACT [30] Foreign Application Priority Data with two or three heads defining one or two peripheral recesses included in a throttled path for the controlled Oct. 21, 1970 Germany ..P 20 51582.6 admission of higlbpressure fluid to a peripheral shoulder on that extremity. An oblique passage, forming part of that fluid path, extends in the region of the [58] i 6 596 14 peripheral shoulder within the body of the working le 0 piston. The selected position of the working piston is maintained by countervailing fluid pressure acting upon a land of this piston, the effective area of that [56] References Cned land being half that of the peripheral shoulder which UNITED STATES PATENTS in a state of balance is subjected to half the countervailin fluid ressure. 597,388 l/l898 Brown, Jr. ..l37/625.6 g p 2,690,192 9/1954 Dannhardt ..137/625.63 10 Claims, 7 Drawing Figures i7! 0 E MW 1 4 7 z 14 l I V, 36 I i ,3 5;, 1 if L I I I 5a ll l9 A I I A, V g M 401/, x '7 [I M/ i y I UL .3 c 47 2 6 f l 1 1 22 I 41/1,. 4/ i 20 5/ 2a /2 44 '38 z 4? 45 i a 370 LOAD PATENTEUHARZTIGB SHEET 10F 4 ill! 0(04 A M Q m 2. N MN \m H lm eniar:

BY 1 an Attorney PATENTEDHARZY I973 SHEET 2 OF 4 Lothar KIRSTEIN men/0r:

(Kn I" Tm PATENTEDmz 7197s SHEET 3 BF 4 Lothar KIRSTEIN lm eniar:

PATENTEDHARZTISTZS 3722,54?

SHEET u 0F 4 Lothar KIRSTEIN Wen/0r:

Attorney PILOT VALVE My present invention relates to a pilot valve wherein a main or working piston, controlling the flow of a hydraulic or pneumatic working fluid to a load, is hydraulically or pneumatically positionable with the aid of a smaller pilot piston responding to a controlling force.

The axial shifting of the main piston in its cylindrical housing is effected by the pressure of a pilot fluid acting upon an external peripheral shoulder of that piston, this pressure being derived from a throttled fluid path between an inlet and an outlet port and being therefore a fraction of the supply pressure available at the inlet port which may or may not be the same as the delivery pressure of the working fluid. In order to stabilize the position of the main or working piston after any change in the controlling force, this piston is subjected to the action of biasing means tending to immobilize it in the housing. The biasing force may be derived from the inlet pressure of the pilot fluid with the aid of a conduit opening onto a land of the main piston facing in the direction opposite that of the aforementioned peripheral shoulder.

The general object of my invention is to provide a compact valve construction in which the working piston is of small axial length and isprovided with a simple channel system traversed by the pilot fluid, this system being constituted by a set of short bores than can be easily' machined.

In accordance with my present invention, an extremity of the main piston is provided with an axial bore accommodating the pilot piston, this extremity also carrying the aforementioned peripheral shoulder dividing it into an enlarged and a reduced portion. The reduced portion is engaged by a sealing member on the housing, such as a metal ring, to define a variablevolume fluid chamber to which pilot fluid is admitted via a branch of its throttled path. A part of this path is constituted by an oblique passage in the shouldered extremity of the main piston, this passage communicating with a peripheral recess of the pilot piston bounded by two axially spaced heads thereof; the oblique passage terminates at opposite sides of a transverse plane through the peripheral shoulder, thereby establishing a short connection between that recess and either the above-identified fluid chamber or one of the ports of the pilot path. This arrangement reduces the volume of the variable chamber, which is permanently filled with the pilot fluid (e.g. oil), with resulting improvement in the dynamic response of the valve. The fractional pressure prevailing in that chamber allows the use of a narrow sealing surface with consequent lowering of frictional resistance, increased sensitivity and reduced hysteresis.

According to another feature of my invention, the pilot piston is hollow so as to form a throughgoing channel which equalizes the pressure at opposite ends thereof in the axial bore of the main piston.

The above and other features of my invention will be described in detail hereinafter with reference to the accompanying drawing in which:

FIG. 1 is an axial sectional view of a first embodiment of my invention;

FIG. la is an enlarged sectional detail view of some of the elements shown in FIG. 1;

FIG. lb is a cross-sectional view taken on the line IBIB of FIG. la;

FIG. 1c is a partial flow diagram for the system of FIG. 1;

FIG. 2 is a view similar to FIG. 1, showing a second embodiment;

FIG. 2a is a detail view analogous to FIG. la but relating to the system of FIG. 2; and

FIG. 2b is a cross-sectional view taken on the line IIB-IIB of FIG. 2a.

The pilot valve shown in FIG. 1 comprises a cylindrical housing 1 with end walls 24, 26 secured thereto by bolts 35, 36. A guide sleeve 3 within the housing surrounds a working piston 4 which is axially slidable therein to admit oil or some other working fluid to a load 37 via one of two ports 38, 39, both ports being cut off in the illustrated centered piston position in which two axially spaced piston heads 4a, 4b obstruct a pair of apertures 10, 11 in sleeve 3 respectively communicating with these ports via ring channels 40, 41. The working fluid delivered by a pump (not shown) enters the housing 1 from the outer surface 2 thereof, as indicated diagramatically by an arrow E, and passes through a further ring channel 42 into an annular recess 43 bounded by piston heads 4a and 4b. With the piston 4 shifted either to the left or to the right, this high-pressure fluid reaches the load 37 through a corresponding entrance duct 380 or 39a to displace it in one sense or the other.

Ring channels 40, 41, 42 are formed by complementary annular grooves in housing 1 and sleeve 3, as are a pair of further ring channels 44, 45 communicating with a low-pressure region or sump via respective discharge ducts diagramatically indicated by arrows D and D. It will be apparent that the establishment of a connection from inlet port 8 to one of the two conjugate working ports 38, 39 places the other of these ports in communication with outlet port 9 or 9' via an associated further peripheral recess 46, 47 of piston 4.

The left-hand extremity of the main piston 4 (as viewed in FIG. 1) is formed with an axial bore 18 accommodating a pilot piston 7, the latter being integral with a stem 21 passing outwardly through wall 26 by way of an enlarged extension 19 of bore 18. Stem 21 is axially shiftable, as indicated by an arrow C, in response to an external controlling force (e.g. that of a solenoid) to displace the piston 7 which has three axially spaced heads 7a, 7b, (see particularly FIG. la) in sliding contact with the wall of bore 18. In the region of this bore, this left-hand extremity is divided by a peripheral shoulder A into a reduced portion 4' and a relatively enlarged portion 4 the latter forming one of the boundaries of peripheral recess 46. This recess, which through port 9 communicates with the low-pressure side of the nonillustrated pump delivering the working fluid to inlet port 8, is connected through a pair of radial bores 14 in piston 4 with a peripheral recess 48 of piston 7 bounded by heads 7b and 7c thereof. A similar recess 49 lies between piston heads 7a and 7b at the left of a transverse plane, coinciding with the section line IB-IB in FIG. la, which passes through the shoulder A. Recess 49 is open toward an oblique bore 13 in the body of piston 4 traversing the plane IB-IB and terminating at a ring channel 50 which communicates with a conduit 12 in housing 1, this conduit in turn being joined to inlet port 8 (as diagramatically indicated in FIG. 10) so as to carry the delivery pressure of the supply pump.

The middle piston head 7b has a width slightly less than the diameter d of an adjoining radial bore 16 which traverses the piston 4 and terminates at a chamber 51 of variable volume bounded by shoulder A and by a sealing ring 5a forming part of a metallic annular profile 5. In the normal relative piston position shown in FIG. 1a, two narrow clearances 27 and 28 are thereby left at opposite sides of head 7b to provide throttled fluid passages of a width equaling each onethirtieth the size of diameter d. By these passages, the pressure difference existing between recess 49 (fed directly by the pump via passage 13) and recess 48 (vented to the sump via bores 14) is halved so that the fluid pressure in chamber 51, acting upon shoulder A, is half the supply pressure communicated from recess 43 via a pair of radial bores 15 to an axial bore 52in the right-hand extremity of piston 4. Bore 52 receives an ancillary piston 6 bearing upon a plug 23 which is screwed into the end cap 24 and is locked in a selected position of adjustment by a counternut 25. The end wall B of bore 52 and the confronting face B of piston 6 have an effective area equaling half that of shoulder A whereby, in view of the aforedescribed pressure relationship, the forces normally acting from opposite sides upon piston 4 are in balance.

A pair of Belleville springs 22, surrounding the profile 5, bear axially upon the sleeve 3 and urge it to the right into contact with plug 23. An adjustable space 53 between end wall 24 and sleeve 3, communicating via radial flutes in the right-hand face of the sleeve with a clearance 54 at the right end of piston 4, is connected to an axially extending chamber 17 within housing 1 which terminates at the vented extension 19 of bore 18 (see FIG. 1c). As best seen in FIG. la, piston 7 has an axial bore 55, surrounding the stem 21 with clearance, and a pair of transverse bores 56 connecting; bore 55 with a similar bore 57 at the free end of the stem, thereby equalizing the pressure on opposite sides of that piston. Thus, both ends of the two pistons 4 and 7 are always under atmospheric or sump pressure.

As will be apparent from FIG. 1b, bore 16 and passage 13 (which are symmetrically duplicated on opposite sides of the piston axis) lie in mutually perpendicular planes even though, for convenience, they have been shown coplanar in FIGS. 1 and 1a. Radial bores 14 and 56 lie in the same plane as the oblique passages 13.

In operation, any unbalancing of the system by a shift of piston 7 to the left from its normal position relative to piston 4 (FIGS. 1 and 1a) reduces the clearance 27 and increases the clearance 28, thereby lowering the fractional pressure prevailing in bores 16 and chamber 51. This results in a fluidpressure differential driving the piston 4 to the left until balance is re-established; fluid from inlet port 8 now reaches the working port 38 to feed the left-hand supply conduit 38a ofload 37. At the same time, the right-hand conduit 39a is vented to the sump through ports 39 and 9'.

Conversely, if the pilot piston 7 is displaced to the right, the increase in passage 27 with concurrent reduction or elimination of passage 28 augments the fluid pressure in chamber 51 and drives the piston 4 to the right (as viewed in FIGS. 1 and la), thereby connecting inlet port 8 with working port 39 and working port 38a with outlet port 9 to move the load in the opposite direction; the flow of working fluid is again cut off upon the re-establishment of the illustrated balanced position.

In FIGS. 2, 2a and 2b I have shown a partial modification of the system described above, corresponding elements having been designated by the same or analogous reference characters. In this case the smalldiameter portion 104' and the large-diameter portion 104" of piston 104 are separated by a shoulder A lying in a transverse plane parallel to section line IIB-IIB, in lieu of the frustoconical shoulder A of the first embodiment. The single pair of aligned radial bores 16, coacting in that embodiment with the middle head 7b of a three-headed pilot piston 7, has been replaced by two pairs of axially spaced bores 33, 34 co-operating with respective heads 7a, 7b of a two-headed pilot piston 7'. As will be apparent from FIG. 2b, bores 34 (and 33) lie in a plane perpendicular to that of a pair of oblique passages 13', one of these passages having been turned into the plane of the bores (with one bore 34 omitted) in FIGS. 2 and 2a to simplify the drawing. The internal construction of piston 7 and its connection with stem 21 is similar to that of piston 7 in the preceding Figures.

As indicated by arrows F and G in FIG. 2, high-pressure fluid enters a pair of radial bores 29 in sleeve 3 through the housing 1 and is drained to the sump by way of similar bores 30 which are axially offset therefrom. Piston portion 104" has two axially spaced peripheral recesses 50, 50" respectively communicating with bores 29 and 30. These bores may be included in a fluid circuit independent of that for the working medium, with a supply pressure unaffected by possible pressure variations in the load circuit; if this separation is not necessary, however, bore 29 may also communicate with bore 8 via internal channels not shown. In any event, the fluid pressure built up in recess 50 is transmitted by way of radial bores 31 in piston 104 and an axial bore 32 to an enlarged extension 52' of the latter bore receiving the ancillary piston 6. Owing to the presence of central bore 32, a part B, of the end face of bore 52' has been relocated to the region of piston portion 104"; however, the combined effective area of this port B and the remainder B,,, upon which the fluid pressure acts in a leftward direction, remains unchanged. This area, therefore, is again half the size of the effective area of shoulder A bounding a chamber 51' of variable volume which communicates through passages 13' with a peripheral recess 48' of piston 7' defined by its heads and 7b. The separation of these heads slightly exceeds the spacing of bores 33 and 34 whereby clearances 27' and 28' are normally present at these bores to form throttled passages for admitting fluid to recess 48' from space 50' at half the supply pressure symbolized by arrow F and for draining the fluid from recess 48' by way of space 50" at zero pressure as symbolized by arrow G. Thus, the fractional pressure prevailing in recess 48 is transmitted by way of passage 13' to the chamber 51' so as to balance exactly the fluid force acting upon area B 8,, when the two pistons are in their normal relative position shown in the drawing, i.e. when clearances 27' and 28' are equal with a width again corresponding to 1/30 of the diameter d of the associated bores (here the bores 33 and 34). In this embodiment, therefore, the oblique passages 13' constitute the branch of the pilot-fluid path serving for the transmission of the fractional fluid pressure to piston shoulder A.

The system of FIG. 2 responds to a displacement of stem 21 in the same manner as that of FIG. 1.

It will be apparent that the fluid channels best illustrated in FIGS. 1a and 2a can be machined in a simple manner and accommodated on a small part of the main piston 4 or 104, thanks mainly to the presence of the oblique passages 13 or 13' which terminate on opposite sides of a transverse plane passing through shoulder A or A. This compact design also minimizes the axial length of the small-diameter piston portion 4' or 104' engaged by the seal 5, thereby also reducing the volume of the fluid chamber 51 or 51' subjected to fractional pressure. With separation of the working and pilot circuits, as discussed above with reference to FIG. 2 but evidently also possible in the system of FIG. 1, the pressure in that chamber can be made as low as desired so that the contact area between the seal and the piston may also be small, along with the frictional resistance generated therein. This results in a highly sensitive value with minimum hysteresis.

I claim:

1. A pilot valve comprising:

a cylindrical housing provided with a channel system for the flow of a working fluid to a load; main piston axially movable in said housing for selectively blocking and unblocking the flow of said working fluid, said main piston having an extremity provided with an axial bore and with an external peripheral shoulder in the region of said bore; sealing means in said housing bearing upon a reduced portion of said extremity and defining a fluid chamber with said shoulder;

a pilot piston axially slidable in said bore, said pilot piston being provided with a plurality of heads defining at least one peripheral recess included in a throttled path extending between a high-pressure port and a low-pressure port with a branch terminating at said fluid chamber for exerting upon said shoulder a fractional fluid pressure controlled by the relative position of said pistons, said path including an oblique passage in said extremity communicating with said recess and terminating at opposite sides of a transverse plane through said shoulder; and

biasing means tending to immobilize said main piston in said housing.

2. A pilot valve as defined in claim I wherein said biasing means comprises a land on said piston facing in a direction opposite that of said shoulder, said land being subjected to a countervailing fluid pressure from said high-pressure port.

3. A pilot valve as defined in claim 2 wherein the effective area of said land is half that of said shoulder, said fractional fluid pressure being half said countervailing fluid pressure in a state of fluidic balance.

4. A pilot valve as defined in claim 3 wherein said pilot piston has three axially spaced heads defining between them a first recess and a second recess, said first recess being open toward said passage and communicating therethrough with said high-pressure port, said second recess communicating with said low-pressure port, said branch bein a radial bore in said extremi y confronting the m1 dle one of said heads and defining two narrow clearances on opposite sides thereof in a normal relative position of said pistons.

5. A pilot valve as defined in claim 4 wherein said first recess is surrounded by said reduced portion of said extremity, said passage terminating at an enlarged portion separated by said shoulder from said reduced portion.

6. A pilot valve as defined in claim 3 wherein said pilot piston has two axially spaced heads bounding said recess, said branch being constituted by said passage, said recess normally communicating with said ports via two radial bores in said extremity partly obstructed by' said heads with formation of two narrow clearances.

7. A pilot valve as defined in claim 6 wherein said radial bores terminate at an enlarged portion of said extremity separated by said shoulder from said reduced portion.

8. A pilot valve as defined in claim 1 wherein said pilot piston has a throughgoing channel for equalizing the pressure in said axial bore at opposite ends thereof.

9. A pilot valve as defined in claim 1, further comprising a guide sleeve in said housing surrounding said main piston, said sleeve being provided with apertures forming part of said channel system.

10. A pilot valve as defined in claim 9, further comprising adjustable abutment means for said sleeve and resilient means axially urging said sleeve into contact with said abutment means. 

1. A pilot valve comprising: a cylindrical housing provided with a channel system for the flow of a working fluid to a load; a main piston axially movable in said housing for selectively blocking and unblocking the flow of said working fluid, said main piston having an extremity provided with an axial bore and with an external peripheral shoulder in the region of said bore; sealing means in said housing bearing upon a reduced portion of said extremity and defining a fluid chamber with said shoulder; a pilot piston axially slidable in said bore, said pilot piston being provided with a plurality of heads defining at least one peripheral recess included in a throttled path extending between a high-pressure port and a low-pressure port with a branch terminating at said fluid chamber for exerting upon said shoulder a fractional fluid pressure controlled by the relative position of said pistons, said path including an oblique passage in said extremity communicating with said recess and terminating at opposite sides of a transverse plane through said shoulder; and biasing means tending to immobilize said main piston in said housing.
 2. A pilot valve as defined in claim 1 wherein said biasing means comprises a land on said piston facing in a direction opposite that of said shoulder, said land being subjected to a countervailing fluid pressure from said high-pressure port.
 3. A pilot valve as defined in claim 2 wherein the effective area of said land is half that of said shoulder, said fractional fluid pressure being half said countervailing fluid pressure in a state of fluidic balance.
 4. A pilot valve as defined in claim 3 wherein said pilot piston has three axially spaced heads defining between them a first recess and a second recess, said first recess being open toward said passage and communicating therethrough with said high-pressure port, said second recess communicating with said low-pressure port, said branch being a radial bore in said extremity confronting the middle one of said heads and defining two narrow clearances on opposite sides thereof in a normal relative position of said pistons.
 5. A pilot valve as defined in claim 4 wherein said first recess is surrounded by said reduced portion of said extremity, said passage terminating at an enlarged portion separated by said shoulder from said reduced portion.
 6. A pilot valve as defined in claim 3 wherein said pilot piston has two axially spaced heads bounding said recess, said branch being constituted by said passage, said recess normally communicating with said ports via two radial bores in said extremity partly obstructed by said heads with formation of two narrow clearances.
 7. A pilot valve as defined in claim 6 wherein said radial bores terminate at an enlarged portion of said extremity separated by said shoulder from said reduced portion.
 8. A pilot valve as defined in claim 1 wherein said pilot piston has a throughgoing channel for equalizing the pressure in said axial bore at opposite ends thereof.
 9. A pilot valve as defined in claim 1, further comprising a guide sleeve in said housing surrounding said main piston, said sleeve being provided with apertures forming part of said channel system.
 10. A pilot valve as defined in claim 9, further comprising adjustable abutment means for said sleeve and resilient means axially urging said sleeve into contact with said abutment means. 